1. Field of the Invention
The present invention relates to an inkjet image forming apparatus in which a head maintenance operation is performed, and to a head maintenance method.
2. Description of the Related Art
An inkjet image forming apparatus, such as an inkjet printer, has a recording head configured to discharge droplets of a recording fluid, such as ink, via a plurality of small nozzles onto a recording medium, such as a sheet of paper. For discharging the droplets, the recording head may employ various mechanisms, such as a movable actuator mechanism based on a piezoelectric principle, or a thermal mechanism based on film boiling (see Patent Documents 1 through 5, for example).
In such an inkjet image forming apparatus, a maintenance operation is performed as required in order to maintain or recover a proper ink discharging performance of the nozzles in the recording head. The maintenance operation may include capping and recovery. Capping involves capping the nozzles of a recording head with a cap in a non-activated period of the head in order to prevent the clogging of the nozzles due to the drying of the recording fluid, which may result in a decrease in the discharged amount of recording fluid. Recovery includes a blank discharge operation and a “flow-out” operation. In the blank discharge operation, the recording head discharges ink into the cap in a period other than an image formation period. In the flow-out operation, the ink is suctioned out of the nozzles of the recording head into the cap using a vacuum pump, for example.
Although the recovery operation requires a mechanism for ejecting the recording fluid collected in the cap out of the cap, the mechanism is not very complex when there is only one head and one cap. However, when there are multiple heads and the corresponding caps, each cap requires the ink ejecting mechanism so as to eject the ink out of the cap (see Patent Documents 2 and 3), resulting in a more complex structure and an increase in cost.
A conventional technology attempts to overcome the above problem by providing the ink ejecting mechanism to only one of the caps and making the one cap movable so that the movable cap can be moved to whichever recording head is used for blank discharge, and the ink can be discharged into the movable cap. Another technology proposes performing the recovery operation for multiple recording head units successively by moving a cap in one direction (see Patent Document 5, for example).
However, when the recovery operation is successively performed by moving the cap, the standby time between the end of the recovery operation and the start of the next image forming operation varies depending on the position of the recording head. For example, the standby time is longer for the recording head for which the recovery operation is performed first than for the recording head for which the recovery operation is performed last. As a result, the viscosity of the ink in the first recording head may increase to such an extent that the required level of ink discharge performance may not be maintained for the next image forming operation.
Further, the blank discharge operation is associated with the problem of staining of areas around the recording head that has performed blank discharge, such as the nozzles of an adjacent recording head.
Patent Document 6 discloses that two ink receiving units for receiving ink discharged in a preliminary discharge operation are provided at different locations, and one of the ink receiving units is selected depending on the location of the preliminary discharge operation in order to prevent the staining of the interior of the image forming apparatus by the discharged ink. Patent Document 7 discloses that a blocking member is provided for preventing the staining of areas around the recording head by an ink mist produced by the blank discharge operation. Patent Document 8 discloses that a suction recovery operation is performed only for one or more of the recording head units in which an ink discharge defect is present, wherein a separate cap member for the recovery operation is provided.
Patent Document 9 discloses a positioning mechanism for positioning a maintenance unit. Patent Document 10 discloses that the caps are divided into two or more groups, where some of the nozzles can be independently closed by one of the cap groups or all of the caps can be closed by all of the nozzles simultaneously. Patent Document 11 discloses that a blank discharge operation can be performed for a recording head positioned in an area outside the range of the recording sheet by using a movable cap member. Patent Document 12 discloses a structure that enables maintenance of a recording head having a number of nozzles, where ink is suctioned out of the nozzles in a uniform manner.
While the above conventional technologies enable recovery of plural recording head units independently by pressure discharge, suctioning, or blank discharge, none of the technologies address the problem of staining of the recording head adjacent the recording head used for blank discharge by the ink mist produced by the blank discharge and released upon removal of the cap, for example.    Patent Document 1: JP9-70961A    Patent Document 2: JP2009-78539A    Patent Document 3: JP Patent No. 3231144    Patent Document 4: JP2008-290400A    Patent Document 5: JP Patent No. 3670428    Patent Document 6: JP2001-113714A    Patent Document 7: JP2008-307797A    Patent Document 8: JP2006-96017A    Patent Document 10: JP2009-166357A    Patent Document 11: JP Patent No. 2771545    Patent Document 12: JP2008-213216A